Combine harvesters are large agricultural machines that travel through agricultural fields cutting, threshing, separating and cleaning crop plants. They comprise a self-propelled agricultural vehicle with threshing, separating, and cleaning mechanisms. They also comprise cutting mechanisms mounted on the front of the vehicle for cutting and gathering a wide swath of crop and feeding that crop into the threshing, separating and cleaning mechanisms of the vehicle. The vehicle or vehicle and cutting mechanism may be called a “harvester”, a “combine harvester”, an “agricultural combine” or like terms.
The cutting mechanisms are variously called “cutting heads”, “harvesting heads”, “heads”, “headers” or like terms. The headers typically comprise elongated frames that support elongated knives and crop conveyors. The headers can be twenty to forty feet wide. They are typically suspended on, and cantilevered forward from, an elevating crop conveyor or “feederhouse”. The feederhouse is pivotally connected to and extends forward from the chassis or frame of the vehicle.
Headers that are designed to harvest low-lying crop plants like soybeans or wheat must follow the ground very closely so the knives on the header that sever the plant from the ground can reach completely under the plant, sever the plant stalk and substantially the entire plant can be harvested.
The ground in the agricultural fields is not perfectly flat, hence header height control systems are used to automatically raise and lower the header with respect to the vehicle as the combine harvester travels through the field. As the ground rises and falls underneath the header, the header height closed loop control system raises and lowers the feederhouse in response to maintain a constant distance between the header (mounted on the front of the feederhouse) and the ground.
It is difficult to maintain a constant distance between the header and the ground. In recent years, engineers have designed wider and heavier headers. In addition, they have designed vehicles with larger wheels and tires to distribute this increased load more evenly on the ground and therefore reduce ground compaction.
The larger tires act like springs, permitting the vehicle, and hence the header mounted on the front of the vehicle to bounce up and down as the wheels roll over the ground. Even worse, the system is under-actuated as the vehicle wheels can be so soft that they compress in reaction to the header height control system lifting the header and decompress in reaction to the header height control system lowering the header.
In extreme cases, the header height control system and compressible tires can be so bad that the tires of the combine harvester begins to hop completely off the ground as the header height control system becomes unstable.
What is needed is a header height control system that dynamically dampens the response to compensate for the flexibility (i.e. compression and decompression) of the combine harvester tires. It is an object to provide this system. The problem is solved by the arrangement of claim 1, additional features and benefits are provided by the arrangements of the claims dependent on claim 1.